3.14.34-rt32-rc1 stable review patch. If anyone has any objections, please let me know.
------------------ From: Sebastian Andrzej Siewior <[email protected]> This behaviour is required by cpufreq and its logic is "okay": It does a read_lock followed by a try_read_lock. Lockdep warns if one try a read_lock twice in -RT and vanilla so it should be good. We still only allow multiple readers as long as it is in the same process. Cc: [email protected] Signed-off-by: Sebastian Andrzej Siewior <[email protected]> Signed-off-by: Steven Rostedt <[email protected]> --- include/linux/rwsem_rt.h | 1 + kernel/locking/rt.c | 29 +++++++++++++++++++++++------ 2 files changed, 24 insertions(+), 6 deletions(-) diff --git a/include/linux/rwsem_rt.h b/include/linux/rwsem_rt.h index 0065b08fbb7a..924c2d274ab5 100644 --- a/include/linux/rwsem_rt.h +++ b/include/linux/rwsem_rt.h @@ -20,6 +20,7 @@ struct rw_semaphore { struct rt_mutex lock; + int read_depth; #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif diff --git a/kernel/locking/rt.c b/kernel/locking/rt.c index eac2ddea9c45..9a972e996185 100644 --- a/kernel/locking/rt.c +++ b/kernel/locking/rt.c @@ -322,7 +322,8 @@ EXPORT_SYMBOL(rt_up_write); void rt_up_read(struct rw_semaphore *rwsem) { rwsem_release(&rwsem->dep_map, 1, _RET_IP_); - rt_mutex_unlock(&rwsem->lock); + if (--rwsem->read_depth == 0) + rt_mutex_unlock(&rwsem->lock); } EXPORT_SYMBOL(rt_up_read); @@ -333,6 +334,7 @@ EXPORT_SYMBOL(rt_up_read); void rt_downgrade_write(struct rw_semaphore *rwsem) { BUG_ON(rt_mutex_owner(&rwsem->lock) != current); + rwsem->read_depth = 1; } EXPORT_SYMBOL(rt_downgrade_write); @@ -370,12 +372,23 @@ EXPORT_SYMBOL(rt_down_write_nested_lock); int rt_down_read_trylock(struct rw_semaphore *rwsem) { - int ret; + struct rt_mutex *lock = &rwsem->lock; + int ret = 1; - ret = rt_mutex_trylock(&rwsem->lock); - if (ret) - rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_); + /* + * recursive read locks succeed when current owns the rwsem, + * but not when read_depth == 0 which means that the rwsem is + * write locked. + */ + if (rt_mutex_owner(lock) != current) + ret = rt_mutex_trylock(&rwsem->lock); + else if (!rwsem->read_depth) + ret = 0; + if (ret) { + rwsem->read_depth++; + rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_); + } return ret; } EXPORT_SYMBOL(rt_down_read_trylock); @@ -383,7 +396,10 @@ EXPORT_SYMBOL(rt_down_read_trylock); static void __rt_down_read(struct rw_semaphore *rwsem, int subclass) { rwsem_acquire(&rwsem->dep_map, subclass, 0, _RET_IP_); - rt_mutex_lock(&rwsem->lock); + + if (rt_mutex_owner(&rwsem->lock) != current) + rt_mutex_lock(&rwsem->lock); + rwsem->read_depth++; } void rt_down_read(struct rw_semaphore *rwsem) @@ -408,6 +424,7 @@ void __rt_rwsem_init(struct rw_semaphore *rwsem, const char *name, debug_check_no_locks_freed((void *)rwsem, sizeof(*rwsem)); lockdep_init_map(&rwsem->dep_map, name, key, 0); #endif + rwsem->read_depth = 0; rwsem->lock.save_state = 0; } EXPORT_SYMBOL(__rt_rwsem_init); -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
